The present invention relates to a field-emission display having low-speed electron beam phosphor layers for emitting light in response to bombardment of an electron beam applied from field-emission cathodes.
Electron-beam excited field-emission display devices include a vacuum fluorescent display (VFD) employing low-speed electron beam phosphor layers, so-called Aiken and Gerber tubes, a flat display in the form of a secondary electron multiplier, and a display with a matrix drive system.
Most of these displays are energized at a high voltage, and hence it is difficult to lower their power consumption.
The VFDs are low-voltage excited displays. Since the VFDs have not been advanced to a technical level for displaying television images, and have a relatively low resolution, there have been no reports on attempts to produce high-contrast VFDs for displaying high-quality, high-resolution NTSC and high-definition television images.
Research and development efforts have been made with respect to field-emission displays (FEDs) employing field-emission microcathodes which can be energized at a low voltage and have a relatively high resolution.
A flat field-emission display comprises an ultra-thin display panel having microtip cathodes in the form of very small conical cathodes fabricated according to a micro-fabrication process. Electrons are emitted from the microtip cathodes and are applied to excite a confronting phosphor panel to display signals. One such flat field-emission display is schematically illustrated in FIG. 1 of the accompanying drawings.
As shown in FIG. 1, the flat field-emission display has a cathode panel 1 made of glass or the like, and a plurality of cathode electrodes 2 made of Cr or the like which are patterned in stripes on the cathode panel 1. A plurality of gate electrodes 4 made of Mo, W, or the like are patterned as stripes perpendicular to the cathode electrodes 2 on insulating layers 3 which are deposited on the cathode electrodes 2. The cathode electrodes 2 and the gate electrodes 4 have areas of intersection which have a plurality of small holes 5 defined therein, each of the small holes 5 housing a cathode therein.
FIG. 2 of the accompanying drawings schematically shows a cathode arrangement of the flat field-emission display. After the cathode electrodes 2, the gate electrodes 4, and the insulating layers 3 have been successively deposited by sputtering, vacuum evaporation, or the like, holes 5 are defined by wet etching, for example. Thereafter, conical field-emission cathodes 6 made of W or the like are formed in the respective holes 5 by oblique evaporation, sputtering, or the like while the cathode panel 1 is being rotated.
For displaying color images, R (red), G (green), and B (blue) phosphor layers are formed in stripes on transparent electrodes 12 made of ITO (oxide of mixed In, Sn) which are mounted on an inner surface of a front panel 11 made of glass or the like. The panels 1, 11 are then hermetically sealed by a seal member with a spacer having a thickness of several hundreds .mu.m interposed therebetween, thus keeping a certain level of vacuum between the panels 1, 11.
When an electric field having a field intensity ranging from 10.sup.6 to 10.sup.8 V/cm at a voltage ranging from 10 to 100 V is applied between the field-emission cathodes 6 and the gate electrodes 4, electrons are emitted from the tip ends of the cathodes 6. When the confronting transparent electrodes 12 are maintained at a potential of about 300 V, the emitted electrons are applied to the R, G, B phosphor layers, which then emit light to display a color image.
To increase the contrast of the flat field-emission display, a black carbon layer which is used as a black mask in an ordinary cathode-ray tube (CRT) may be included in the flat field-emission display. However, the black carbon layer will cause a short circuit between the R, G, B phosphor layers as the black carbon layer is electrically conductive.
When the insulating layer 3 is bombarded by emitted electrons, if the material of the insulating layer 3 has a high secondary electron emission ratio, then it is charged up to a positive potential, and if the material of the insulating layer 3 has a low secondary electron emission ratio, then it is charged up to a negative potential. Therefore, the emission from the R, G, B phosphor layers varies with time, resulting in an unstable image display. Secondary electrons tend to stray, thus disturbing the electric field.
Another problem is that if a commercially available ordinary black glass paste which is an insulation and is used for screen printing or the like is added for an increased contrast, then the display panel is not made sufficiently black.